Concentrated solar power (CSP) has the potential of fulfilling the world’s electricity needs. Parabolic-trough system using synthetic oil as the HTF with operating temperature between 300 and 400o C, is the most matured CSP technology. A thermal storage system is required for the stable and cost effective operation of CSP plants. The current storage technology is the indirect two-tank system which is expensive and has high energy consumption due to the need to prevent the storage material from freezing. Latent heat storage (LHS) systems offer higher storage density translating into smaller storage size and higher performance but suitable phase change materials (PCMs) have low thermal conductivity, thus hindering the realization of their potential. The low thermal conductivity can be solved by heat transfer enhancement in the PCM. There is also lack of suitable commercially-available PCMs to cover the operating temperature range. In this study, a hybrid cascaded storage system (HCSS) consisting of a cascaded finned LHS and a high temperature sensible or concrete tube register (CTR) stages was proposed and analysed via modelling and simulation. Fluent CFD code and the Dymola simulation environment were employed. A validated CFD phase change model was used in determining the heat transfer characteristics during charging and discharging of a finned and unfinned LHS shell-and-tube storage element. The effects of various fin configurations were investigated and heat transfer coefficients that can be used for predicting the performance of the system were obtained. A model of the HCSS was then developed in the Dymola simulation environment. Simulations were conducted considering the required boundary conditions of the system to develop the best design of a system having a capacity of 875 MWhth, equivalent to 6 hours of full load operation of a 50 MWe power plant. The cascaded finned LHS section provided ~46% of the entire HCSS capacity. The HCSS and cascaded finned LHS section have volumetric specific capacities 9.3% and 54% greater than that of the two-tank system, respectively. It has been estimated that the capital cost of the system is ~12% greater than that of the two-tank system. Considering that the passive HCSS has lower operational and maintenance costs it will be more cost effective than the twotank system considering the life cycle of the system. There is no requirement of keeping the storage material above its melting temperature always. The HCSS has also the potential of even lower capital cost at higher capacities (>6 hours of full load operation).

We present a numerical model of Bridgman crystal growth. Pseudo-incompressibility constraint is used to handle jumps in density during phase change. ALE formulation is employed to account for moving parts of the system. Field equations and movement of material interfaces are decoupled in fractional step manner. Naviér-Stokes problem is extended to solid phase where no flow is enforced by Darcy-like forcing. Latent heat of phase change is added to effective heat capacity as approximate Dirac-$\delta$. Backward Euler discretization in space and P2/P1/P1 in space are used. Transient and stationary solutions are being found and compared to temperatures measured directly inside a steady system. Influence of pull-rates on growth process and shape of phase interface are being examined. Powered by TCPDF (www.tcpdf.org)

Incorporating insulation material with phase change materials (PCMs) could help enhance the insulation capability for a refrigerator system. The phase change material can absorb or release large amount of latent heat of fusion depending on surrounding temperatures for efficient thermal management. This research focuses on how incorporating PCM to the conventional PU foam insulation affects the inside temperatures of the refrigerator system and in-turn helps in conserving energy by reducing the compressor run time. It was found that only 0.25-inch-thick PCM layer in insulation can certainly benefit the refrigerators by reducing the amount of electricity consumption and thus increasing the total energy savings through the numerical study results via COMSOL Multiphysics in this study. This work aims to investigate a PCM-incorporated insulation material to accomplish the enhancement of thermal insulation performance for refrigerators.

Ingeniero Civil / El contexto general del problema que se quiere resolver en este trabajo de titulación está basado en la sustentabilidad aplicada en la construcción. El aporte informativo sobre materiales de cambio de fase PCM (Phase Change Materials) aplicados como materiales de construcción es una de las motivaciones de este trabajo, considerando que no existe más información sobre estos materiales aplicados bajo las características particulares de Chile. Es por ello por lo que se analizará la situación actual del país, con el objetivo de introducir al lector al contexto particular del problema que se busca resolver en el presente trabajo, el cual corresponde a la falta de un modelo de transferencia de calor para materiales de cambio de fase incorporados a ventanas. El objetivo principal de este trabajo de titulación es la implementación de un modelo de transferencia de calor para materiales de cambio de fase que están incorporados a ventanas en espacios de oficina, además se compararan resultados para distintos casos de estudio, incorporando al modelo distintos tipos de PCM, distintos climas, distintas épocas del año y distintas orientaciones de la ventana en el espacio de oficina. La metodología aplicada para desarrollar el trabajo de titulación consiste en una etapa de revisión bibliográfica, definición de las variables del modelo, validación del modelo sin PCM por medio de la comparación de temperaturas de la superficie interior de la ventana modelada en EnergyPlus y en Matlab, implementación de modelo en Matlab con la incorporación de materiales de cambio de fase, cálculo de confort térmico por medio del cálculo de índices como el voto estimado medio PMV (Predicted Mean Vote). Los resultados obtenidos de este trabajo muestran que dependiendo de las características del PCM, como la temperatura de activación o el calor latente del material se logra una mayor o menor reducción en los peaks de temperatura de la superficie de la ventana. En el caso de Santiago se obtiene una reducción del promedio de peaks de temperatura superficial de la ventana de 14°C al comparar un modelo con y sin PCM, esta reducción tiene un impacto en el confort térmico obteniendo una reducción del índice PMV de 1.5 a 0.9, lo cual es una mejora considerable al aplicar materiales de cambio de fase. Se generan resultados para distintos casos como se mencionó anteriormente y se obtienen resultados que indican que incorporar PCM al modelo reduce las temperaturas de la superficie de la ventana y en consecuencia genera una mejora en el confort térmico.

This report aims to study how the indoor climate in a conference room can be improved by the use of phase change material (PCM). The study includes an experiment where 40 kg of salt hydrate based PCM was placed within a conference room located in an office in the city of Uppsala, Sweden. The experiment resulted in a decrease in the peak temperature with respect to the internal heat gains in the conference room and a slower temperature increase with PCM implemented. The report concludes that PCM can improve the indoor climate in regard to its ability to limit the temperature fluctuation. The study also contains modelling and simulation over the office and conference room in the program Trnsys. This was carried out to study how the temperature and cooling demand in the conference room and office respectively would change with a larger implementation of PCM. When 106 kg of PCM was simulated to be implemented in two of the conference room walls, the specific peak temperature was on average decreased with 0.17 °C/kW during the year. Furthermore, a decrease in the cooling demand with 16 % was achieved when implementing 1 208 kg of PCM in the internal walls of the office. This study shows that there is potential for reducing the cooling demand in the building through an implementation of PCM. Further studies with a more detailed model of the office is recommended before deciding upon if and where PCM should be implemented.

O objetivo deste trabalho foi avaliar o efeito da enxertia seriada e micropropagação no rejuvenescimento de matrizes adultas de Tectona grandis. A experimentação foi realizada nas empresas Floresteca S.A e Bioteca Ltda, Mato Grosso, utilizando três materiais genéticos diferente, sendo dois clones, com 35 anos idade e mudas de semente. Como técnica de macropropagação optou-se pela enxertia seriada com delineamento inteiramente aleatorizado com três tratamentos representados pelos materiais genéticos com sete repetições. Para micropropagação, utilizou-se meio MS modificado. O experimento in vitro foi dividido em etapas: resgate do meristema com delineamento inteiramente aleatorizado, com os tratamentos sendo três materiais genéticos com trinta repetições; estabelecimento da cultura com os tratamentos arranjados em fatorial 3x5 sendo três materiais genéticos com cinco concentrações de BAP, totalizando quinze tratamentos com cinco repetições; multiplicação/rejuvenescimento com delineamento inteiramente aleatorizado, com os tratamentos arranjados em fatorial 3x5 sendo três materiais genéticos com cinco subcultivos, totalizando quinze tratamentos com três repetições e enraizamento das microestacas. Para macroprogação, o parâmetro avaliado foi a percentagem de pega dos enxertos. Para micropropagação, na fase de resgate, avaliou-se o número de meristemas viáveis; na fase de estabelecimento da cultura, avaliou-se o tamanho, número de nós e número de folhas dos explantes; e na fase de multiplicação/rejuvenescimento, avaliou-se o desenvolvimento de brotos nos sucessivos subcultivos. Os enxertos das mudas obtidas por semente apresentaram brotação aos sete dias de enxertados comparados aos clones que iniciaram as brotações aos quinze dias de enxertados. A sobrevivência dos meristemas apicais introduzidos que não apresentaram oxidação ou contaminação foi superior a 84%. A concentração de 1,5 mg.L-1 de BAP foi a mais significativa na fase de estabelecimento da cultura. O número de brotação e o rejuvenescimento do material adulto aumentaram à medida que aumentou o número de subcultivos, bem como a percentagem de enraizamento. O estabelecimento de minijardim clonal de Tectona grandis é possível mediante uso de brotações rejuvenescidas in vitro. / The aim of this study was to evaluate the effect of serial grafting and micropropagation in rejuvenation of Tectona grandis. The experiments were carried out in Floresteca SA and Bioteca Ltda. companies, Mato Grosso, using two clones and seedlings. The clones were 35 years old and the seedlings were six months old. Serial grafting was chosen for macropropagation technique on a completely randomized statistical design, with three treatments corresponding to genetic material with seven replications. For micropropagation, solid modified MS medium was used. The in vitro experiment was divided into stages: meristem rescue on a completely randomized design with the treatments corresponding to three genetic material with seven replications; establishment in vitro culture on completely randomized design arranged in 3x5 factorial scheme, corresponding to three genetic material with five concentrations of BAP resulting in fifteen treatments with five replications; multiplication/rejuvenation on completely randomized design arranged in 3x5 factorial scheme, corresponding to three genetic material with five subcultures concentrations of resulting in fifteen treatments with three replications on a completely randomized 3x5 and microcuttings rooting. For macropropagation, the parameter evaluated was the percentage of grafting takes. For micropropagation, in the rescue phase, it was evaluated the number of viable meristems. In the establishment phase of culture, the parameters evaluated were the size, number of nodes and number of leaves of the explants; and in the phase of multiplication/rejuvenation it was evaluated the development of the shoots in successive subcultures. The shoots sprouting from seedlings grafts at seventh day compared with grafted clones that started sprouting on the fifteenth day after grafting. The survival of apical meristems without oxidation or contamination was above 84%. The concentration of BAP (1.5 mg.L-1) that was the most significant in the establishment phase of culture. The number of shoots produced and the rejuvenation process increases with increasing number of subcultures, as well as the percentage of rooting. The establishment of clonal minigarden of Tectona grandis coud be possible through rejuvenation of trees in vitro.

Conventional heat transfer enhancement methods have focused on the surface characteristics of the heat-exchanger. The enhancement of heat transfer through altering the characteristics of the working fluid has become a new subject of interest. Micro-encapsulated phase change material (MEPCM) slurries show improved heat transfer abilities compared to single phase heat transfer fluids such as water due to their higher specific heat values in their phase change temperature range. The present work is a numerical and experimental study towards fundamental understanding of the impact of using PCM on thermal and fluid flow characteristics of different single-phase and two-phase heat transfer applications. The mathematical formulation to represent the presence of single and multi-component MEPCM is developed and incorporated into the numerical model for single-phase and two-phase fluid flow systems. In particular, the use of PCM in its encapsulated form for heat transfer enhancement of liquid flow in the presence of evaporation is explored. In addition, an experimental study is conducted to validate the numerical model in a setting of natural convection flow. Finally, the application of PCM in its layered form on the effectiveness of drying of moist porous materials (e.g. paper) is investigated.

In recent decades, much research has investigated the efficiency of Phase Change Materials (PCMs) in improving the thermal performance of buildings and pavements. In buildings, increasing the thermal inertia of structural elements by incorporating PCMs decreases the energy required to keep the inside temperature in the comfort range. In concrete pavements, using PCMs decreases the number of freeze/thaw cycles experienced by the pavement and thus increases service life. However, PCMs cannot be added to cementitious binders directly, because they interfere with the hydration reactions between cement and water that produce strength-bearing phases. Therefore different carriers have been proposed to indirectly incorporate PCMs in cementitious materials. Lightweight Aggregate (LWA) is one of the materials that has been proposed as PCM carrier agent. However, it was not studied in depth before. Various experiments were conducted to investigate the problems associated with incorporating LWA presoaked in PCM in cementitious media. The results show that a portion of PCM leaks out of the LWA’s structure and subsequently affects different chemical, physical, and mechanical properties of the binder. In addition, the applicability of Rice Husk Ash (RHA), a common material never before used to encapsulate PCM, as a PCM carrier agent was investigated. The results show that RHA can absorb and contain liquids in its porous structure; and regarding its compatibility with the cementitious media, it can be used as PCM carrier. Different computational simulations using Typical Meteorological Year data were conducted to evaluate the efficiency of PCMs in improving the thermal performance of buildings. Utilizing PCM-incorporated gypsum boards was shown to be a promising strategy to achieve the governmental plans of “Zero Net Energy� buildings. The results show that using a PCM with a melting point near the occupant comfort zone delays and reduces the inside peak temperature, increases the duration of time during which the inside temperature stays in the comfort zone, and decreases the cost and energy required by HVAC system to keep the inside temperature in this range. However, PCMs’ efficiency is completely dependent on the input temperature profile.

Salt hydrates have the potential to be used in heat storage as both phase-change materials (PCMs) and thermochemical materials (TCMs). These materials offer advantages over traditional heat storage methods due to their high energy densities. However, both domestic and industrial applications require thousands of thermal cycles and there are often many issues that need to be overcome before these materials can be used reliably for heat storage. One of the major issues with using salt hydrates as PCMs is incongruency - the formation of anhydrous phases during melting. In this research, the mechanisms of the action of polymers to prevent incongruency in sodium acetate trihydrate have been investigated. A new polymorph of anhydrous sodium acetate, Form IV, was obtained in the presence of the polymer. This polymorph crystallises as long, blade-shaped crystals, thereby increasing the surface area to volume ratio. Indexing of the crystal faces revealed that every face had Na+ or the oxygen atoms of the acetate ion near or on the surface, as opposed to hydrophobic methyl groups found on the faces of the anhydrous salt grown without polymer. These two factors are believed to significantly increase the dissolution kinetics. This technique has the potential to be used for screening polymers to reformulate other salt hydrates that display incongruent behaviour. Eutectic compositions of NaCl and KCl with strontium hydroxide octahydrate were investigated as a potential means to prevent the incongruency of this PCM. However, degradation was observed with thermal cycling. Variable temperature PXRD studies discovered a new Sr(OH)2 hydrate when heating above 75 °C - Sr(OH)2. ⅓H2O. The recrystallisation of the octahydrate from the new phase was slow with incomplete conversion, explaining the degradation with continuous cycling. The effect of addition of NaCl and KCl to congruent barium hydroxide octahydrate was also investigated. On heating, a phase transition was observed, but the samples remained solid. Variable temperature PXRD investigations discovered that this was due to the formation of the salt hydrate, Ba(OH)Cl.2H2O. This hydrate melted at 110 °C, showing its potential as a high temperature PCM. The dehydration pathways of magnesium sulfate heptahydrate were investigated. In-situ PXRD studies showed that changing the heating rate changed the intermediates present during the dehydration. The fast dehydration rate saw both the known phases of trihydrate and 2.5 hydrate form as the dehydration product of the tetrahydrate. These both then dehydrated to the known dihydrate. This differed when the slower heating rate was used, as the trihydrate was the only product of dehydration from the tetrahydrate. The trihydrate then proceeded to dehydrate to a new phase. This was found to be a new polymorph of the dihydrate, β-MgSO4.2H2O. Dehydration of MgSO4.7H2O with 50 mol% NaCl was also performed. Loeweite, Na12Mg7(SO4)13.15H2O, a dication sulfate hydrate, was formed as the major intermediate. This mixture showed advantages over the pure MgSO4.7H2O as dehydration to the monohydrate took less time and occurred at a lower temperature. There were also three fewer intermediate phases before dehydration to the monohydrate. Suspension and encapsulation materials were used in order to overcome the major issue of agglomeration with magnesium sulfate. Liquid water was ruled out as a viable hydration medium. Apparatus was developed to test humidity cycling, which allowed the effects of dehydration time and temperature to be investigated, as well testing a range of different formulations.

There is a current requirement for technologies that store heat for both domestic and industrial applications. Phase-change materials (PCMs) represent an important class of materials that offer potential for heat storage. Heat-storage systems are required to undergo multiple melt/freeze cycles without any change in melting-crystallisation point and heat output. Salt hydrates are attractive candidates on account of their high energy densities, but there are issues associated with potential crystallisation of lower-hydrates, long-term stability, and reliable nucleation. An extensive review of the PCMs in the literature, combined with an evaluation of commercially available PCMs led to the conclusion that many of the reported PCMs, lack at least one of the key requirements required for use as a heat-storage medium. The focus of this research was therefore to identify and characterise new PCM compositions with tailored properties. New PCM compositions based of sodium acetate trihydrate were developed, which showed improved properties through the use of selective polymers that retard the nucleation of undesirable anhydrous sodium acetate. Furthermore, the mechanism of nucleation of sodium acetate trihydrate by heterogeneous additives has been investigated using variable-temperature powder X-ray diffraction. This study showed that when anhydrous Na2HPO4 was introduced to molten sodium acetate trihydrate at 58°C the hydrogenphosphate salt is present as the dihydrate. On heating to temperatures in the range 75-90°C the dihydrate was observed to dehydrate to form anhydrous Na₂HPO4. This result explains the prior observation that the nucleator is deactivated on heating. The depression of melting point of sodium acetate trihydrate caused by the addition of lithium acetate dihydrate has also been investigated using differential scanning calorimetry and powder X-ray diffraction. It has been possible to tune the melting point of sodium acetate trihydrate thereby modifying its thermal properties. Studies of the nucleation of sodium thiosulfate pentahydrate, a potential PCM, led to the structural characterisation of six new hydrates using single crystal Xray diffraction. All of these hydrates can exist in samples with the pentahydrate composition at temperatures ranging from 20°C to 45°C. These hydrates are: α-Na₂S₂O₃·2H₂O, which formed during the melting of α-Na₂S₂O₃·5H₂O; two new pentahydrates, β-Na₂S₂O₃·5H₂O and γ-Na₂S₂O₃·5H₂O; Na₂S₂O₃·1.33 H₂O, β-Na₂S₂O₃·2H₂O and Na₂S₂O₃·3.67 H₂O, which formed during the melting of β- Na₂S₂O₃·5H₂O. Furthermore, new PCMs in the 75-90°C range were identified. The commercial impact and route to market of several of the PCMs are discussed in the final chapter.